ST. PETERSBURG — State environmental officials have asked the city to place a deed restriction on Tropicana Field, one of two key sites in a planned $1.2-billion downtown redevelopment, because soil beneath the dome's asphalt parking lots is contaminated.

But a spokesman for the city said Tuesday the request from the Florida Department of Environmental Protection is voluntary.

The city instead will continue monitoring a 10- to 12-acre section of contaminated soil to the east of the domed stadium. The site is the former home of a municipal gas manufacturing plant.

"We're not interested in pursuing something that appears to be voluntary on our part," said Mike Connors, the city's internal services administrator. "We plan to continue the monitoring program the city and DEP agreed to."

The state agency first made the request for a deed restriction in 2000. It is being renewed as the city considers selling the 86 acres to a developer as part of the Tampa Bay Rays' plan to build a $450-million stadium on the downtown waterfront.

Pamala Vazquez, a DEP spokeswoman, said the agency would not comment on the environmental requirements of a possible redevelopment until a formal application is submitted.

She also said she did not know if the proposed deed restriction would apply to the entire 86-acre property or only a portion of it.

"Until we have a formal permit application in house, we don't speculate about a property or what someone might want to do or what they might be able to do," Vazquez said.

The two developers bidding to purchase Tropicana Field have known that parts of the 86-acre property are contaminated by a former gas manufacturing plant. But the extent of the contamination has been left open to much speculation.

The city, and to a certain extent the prospective developers, have said the environmental damage remaining on the property is minimal.

People opposing the redevelopment and the larger plan to build a $450-million stadium downtown suggest the impact — and potential cost of the cleanup — is much greater.

Vazquez said the Tropicana Field site is currently permitted for industrial use. If the city or a developer wished to change that use, the state would need to sign off on the plans, Vazquez said.

The city is considering proposals to turn the 86-acre stadium property into a mix of retail, residential and office buildings.